The telecommunications industry commonly uses optical fibers to transmit large amounts of data in a short time. One common light source for optical-fiber communications systems is a laser formed using erbium-doped glass. One such system uses erbium-doped glass fibers to form a laser that emits at a wavelength of about 1.536 micrometer and is pumped by an infrared source operating at a wavelength of about 0.98 micrometer. One method usable for forming waveguides in a substrate is described in U.S. Pat. No. 5,080,503 issued Jan. 14, 1992 to Najafi et al., which is hereby incorporated by reference. A phosphate glass useful in lasers is described in U.S. Pat. No. 5,334,559 issued Aug. 2, 1994 to Joseph S. Hayden, which is also hereby incorporated by reference. An integrated optic laser is described in U.S. Pat. No. 5,491,708 issued Feb. 13, 1996 to Malone et al., which is also hereby incorporated by reference.
To increase signal-carrying bandwidth, an optical fiber can carry a plurality of different wavelengths (i.e., colors), wherein each wavelength is modulated (e.g., using amplitude modulation) with a different signal stream. Dense wavelength-division multiplexing (DWDM) is the name for one such scheme wherein each signal stream is modulated on a carrier wavelength that is close to, but slightly different than, the neighboring wavelengths. For example, the carrier wavelengths can be chosen in the infrared at, say, 1536 nm, 1536.8 nm, 1537.6 nm, etc., for a wavelength spacing of 0.8 nm per channel. Many such wavelengths/channels can be combined and transmitted on a single optical fiber. Since photons have extraordinarily low or no interaction with one another, these channels are transmitted with no crosstalk or other interchannel interference. Further, a broadband light amplifier can be used to simultaneously amplify all the colors/channels by equal amounts, also without introducing crosstalk. The challenge, thus, is to be able to separate the channels (i.e., to split off each channel's color without also getting interfering light signals from adjacent channels' colors).
It is desirable to be able, at, for example, a building in downtown Minneapolis, to extract one channel from the plurality of optical channels of data carried on a single optical fiber, e.g., to extract a first data stream that is modulated on the 1536.8 nm channel from all the other channels on some single optical fiber, and to insert in its place a second data stream that is modulated on the 1536.8 nm channel. The remaining channels being transmitted on the optical fiber should be undisturbed. This allows data that has a destination in that building to be separated and delivered into that building, and for other data in the second data stream to be sourced from that building and sent elsewhere.
There is a need in the art for an integrated optical system, including one or more high-powered lasers along with routing and other components, that can be inexpensively mass-produced. The system should be highly reproducible, accurate, and stable. There is further a need to having improved delivery of pump light to the active waveguides. There is further a need for improved add-drop devices that permit extraction of a first signal stream at a first wavelength from a plurality of other signal wavelengths, and insertion of a second signal stream modulated onto a laser carrier of the first wavelength.